@border: 5px + 5;

div {
  width: 125px * 2 - 50;
  height: 100px * 2;
  border: @border solid red;
}

html {
  font-size: 50px;
}

p {
  width: (82rem / 50);
  height: (82 / 50rem); // 除法要放到小括号中
  background-color: (#ffffff / 2);
  border: 5px solid blue;
}
